A. We are studying the molecular mechanisms by which estrogens and antiestrogens specifically alter growth of human breast cancer. 1. We have introduced viral and cellular onc genes (ras and myc) into human breast cancer cells. These retroviruses are stably integrated and viral mRNA is expressed at high levels. Ras induces a hormone independent phenotype. This occurs through increased secretion of several specific growth factors in an autonomous fashion. 2. We are using the technique of differential hybridization to identify specific estrogen regulated genes for cloning and subsequent analysis. We have identified several unique genes induced within 6 hours by estradiol. We have also identified a gene which is specifically induced by antiestrogens and de- induced by estrogen stimulation. 3. We have identified and partially purified several estrogen induced growth factors which are secreted by breast cancer cells into the medium. These include TGF alpha, EGF, IGF-1, TGF beta, PDGF a and PDGF b. In addition we have identified a new approximately 60K growth factor which stimulates clonogenic proliferation of epithelial cells. A very extensive series of investigations are underway probing the range of expression, regulation and pathophysiologic significance of these activities. Among the techniques we are using are antibodies against these growth factors or their receptors, antisense transfections, and growth factor antagonists.